Snap action capacitive type switch

ABSTRACT

Electrical signaling device in the form of a capacitor or condenser having a fixed plate and a generally dome-shaped snap action plate which may be deformed toward the fixed plate, wherein the dome-shaped plate, when in its normal or relaxed state, is in the form of a hollow geometric solid having an open polyagonal base with a planar side wall extending from each side of the base at equal angles thereto toward each other and are joined by an arcuate surface, the base having arcuate corners bent to extend from the opposite side of the base as the side walls. When the number of sides equals three, it has a base which has the general shape of an equilateral triangle with apexes which are arcuate, the latter being bent angularly to the general plane of the plate, forming abutments which resist the deforming force applied to the dome-shaped plate.

United States Patent [1 1 Hansen [451 Aug. 7, 1973 [73] Assignee:Colorado Instruments, Inc.,

Broomfield, C010.

[22] Filed: Aug. 30, 1971 [2]] Appl. No.: 175,941

Wray C. Hansen, Arvada, C010.

[52] US. Cl. 200/52 R, 200/D1G. 1, 200/166 Bl-l, l79/100.4l B, 307/88ET, 317/249 R [51] Int. Cl. H011! 35/00, G080 5/00 [58] Field of Searchl79/l00.4l B, 90 R; 200/D1G. l, 159 B, 181, 52 R, 166 BH;

317/249 R; 307/88 ET Primary Examiner--.l. R. Scott A ttorney-- Gary D.Fields et a1.

[57] ABSTRACT Electrical signaling device in the form of a capacitor orcondenser having a fixed plate and a generally domeshaped snap actionplate which may be deformed toward the fixed plate, wherein thedome-shaped plate, when in its normal or relaxed state, is in the formof a hollow geometric solid having an open polyagonal base with a planarside wall extending from each side of the base at equal angles theretotoward each other and are joined by an arcuate surface, the base havingarcuate corners bent to extend from the opposite side of the base as theside walls. When the numberof sides equals three, it has a base whichhas the general shape of an equilateral triangle with apexes which arearcuate, the latter being bent angularly to the general plane of theplate, forming abutments which resist the deforming force applied to thedome-shaped plate.

7 Claims, 9 Drawing Figures PAIENIEDAHB W 3.751.612

INVENTOR WRAY C. HANSEN wan, 60 714% ATTORNEYS BACKGROUND OF THEINVENTION Application of James R. Webb and Richard C. Webb, forCapacitive Electrical Signal Device and Keyboard Using Said Device",Ser. No. l3,09l, filed Feb. 20, 1970, which issued on Mar. 28, 1972, asU. S. Pat. No. 3,653,038, discloses an electric signal device of acapacitive nature. A metallic target which may or may not have apermanently charged dielectric material mounted on its upper surface islocated beneath a semihemispherical dome spring. Located above the domespring is a push button or key element which, when depressed, changesthe separation distance between the dome spring and the target in a snapaction manner. This action causes a rapid decrease in the voltagebetween the target and the dome spring which decrease is in the form ofa signal pulse. Such application also discloses splitting the targetinto two or more segments and connecting the segments to a plurality ofelectrical signal devices in a matrix arrangement. The keys or pushbutton elements'are mounted in a keyboard arrangement such that whenindividual keys are depressed, coded symbols which represent informationabout the depressed key are generated. The coded symbols are suitablefor direct entry into digital data systems, displays and/or computers.

SUMMARY OF THE INVENTION This invention contemplates. the utilization ofall features of the application just referred to which are applicablethereto and differs therefrom by certain features, including; g

a. The shape and construction of the dome spring which, rather thanbeing in the form'of a circular disk, is in the form of a hollowgeometric solid having an open polyagonal base with a planar side wallextending from each side of the base at equal angles thereto toward eachother and are joined by an arcuate surface, the base having arcuatecorners bent to extend from the opposite side of the base as the sidewalls. Two distinct advantages accrue from this novel construction.First, amore rapid snap-through of the movable plate is obtained than ispossible with the conventional dome shape and the clearanceprovidedunder the side' walls between the arcuate corners allows for the escapeof air under the dome during the snap-through thereof to provide=a morerapid change inplate spacing. It is the rate of change in the capacitivespacing which creates a usable output signal; In one form oftheinvention, the

spring has a basein the shape of an equilateral triangle (delta shaped),the regions at theapexes being circular. These regions are bent at anangle to the general plane of the spring, forming a three point supportwhich resists the deforming forcev applied to the spring. It, like thecircular disk referred to, is of the snap action type, which returns toits original shape when the deforming force is discontinued. Portions ofthe spring extending from the edges of the base and vtoward thegeometrical center of the spring are substantially flat and are joinedby spherical portions,

b. when a plurality of targets are employed for each spring, they arepreferably in the form of concentric rings, rather than pie-shapedsegments, as disclosed in the application referred to,

cithe major areaof one face of the dome spring is preferably attacheddirectly to one end of a cylindrical resilient member carried by a pushbutton key element, as by cementing. Such resilient member is preferablyconstructed of sponge-like material, exemplary of which is polyurethane,and

d. each switch is formed as an individual module comprising a squareparallelepiped housing, a key or button slidable therein, its attachedcylindrical spring of foam material and the dome spring cemented to thelatter. The modules may be disposed in abutting relation, or spaced asdesired, on a printed circuit board which is formed with targets indesired positons thereon.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a plan ofa punch for making adome spring;

FIG. 2 is a section taken on line 2-2, FIG. 1;

FIG. 3 is a section like FIG. 2, illustrating the die with which thepunch cooperates;

FIG. 4 is a section like FIG. 3, illustrating progress of movement ofthe punch into the die;

FIG. 5 is another section of FIGS. 3 and 4, illustrating furtherprogress of movement of the punch into the die;

FIG. 6 is a central section of a module, taken on line 6-6, FIG. 7;

FIG. 7 is a top plan and section taken on line 7-7, FIG. 6;

FIG. 8 is a section taken on line 8-8, FIG. 7; and

FIG. 9 is a plan of an alternative form of target.

DESCRIPTION OF PREFERRED EMBODIMENTS The shape of a preferred form ofthe dome spring, which forms one of the more important features of theinvention, may be best understood by a description of the apparatus andmethod of making same, with reference to FIGS. 1-5.

Punch 10 may be formed of cylindrical rod with one end machined to aspherical surface 12 having a radius R. A circular chamfer 14 is thenformed at the periphery of the spehrical radius and the punch is thenmachined to the cross section shown in FIG. 1, that is, by machining itto provide three flats 16 at equal angles to each other. Three portionsof the spherical end are then machined to form flat surfaces 18 whichform three straight edges 20 with flats l6 andintersect with sphericalsurface 12. These edges 20 are disposed slightly below the plane of theoutermost edge of cham'-' fer 1'4.

The die 22 is formed with a parallelepiped aperture 24 of a shapecorresponding to the cross-sectional shape of the punch but differs frommany conventional blanking dies in that it is formed of twoal'ignedportions 22a, 22b between which flat stock 26 may be clampedaround the periphery of the punch and die aperture.

In the formation of the dome spring, flat stock 26 is immovably clampedbetween dies 22a,22b so that it cannot deform in the radial direction ofthe punch and die. As the punch advances toward the blank, its centralportion first contacts the blank (FIG. 3), commencing its deformation tocorresponding shape. The flat portions 18 next engage the blank anddeform it to corresponding shape. As this continues, the three chamfersengage the blank (FIG. 4) forming three downturned feet or abutments 28.Slight further motion starts the shear of these feet, deformation of thespherical and adjacent flats continuing. When complete shear occurs(FIG. 5) the spherical and flat portions have been deformed to theirfinal shape. The

three straight edges of the punch then engage the blank in theconventional manner of blanking punches and shear the spring 30 to theshape illustrated in FIG. 1 which is in the form of a hollow geometricsolid having an open polyagonal base, such as triangular, with planarside walls extending from each side of the base at equal angles theretotoward each other are joined by an arcuate surface, such as sperical.Each of the three feet 28, bent angularly to the general plane of thespring, bridges a tip of the spherical portion and the outer portions ofadjacent flats 18, forming three reinforced zones and about which thegeneral plane of the spring may buckle to its snap-over position byapplication of a force to its upper or convex surface, the springreturning to its normal position, upon removal of the buckling force. Itwill be understood that the punch may be constructed to form a springhaving a polyagonal base with more than three sides, if desired.

To better enable those skilled in the art to practice the inventionwithout experimentation, the following dimensions and specifications areset forth:

R =4.900" G =0.016" A 0.570" H 0.165" B 0.650" Angle l angle C 36 30'Depressing Force 70-90 grams D 0.018" E 0.011" F 0.14"

Material: stainless steel, N0. 302, full hard, 0.0023 i 0.002 inchthick, tensile strength 180,000 psi, yield strength 140,000 psi,45Rockwell C.

As will be apparent from the above, since E and F differ by 0.003inch-and the stock is approximately 0.025 inch shearing of the threechordal sides commences about the same time that complete shearing ofthe feet is completed. It will, of course, be understood that the entireforming and shearing operations occur in a fraction of a second, as isconventional in punch press operation.

Referring now to FIG. 6, module 32 comprises a square housing 34 havinga cylindrical bore 36 therein which slidably receives a cylindricalflange 38 formed integrally with push button 40. Projections 42 (FIG. 7)engage in grooves 44 to prevent rotation of the button relative to thehousing. Cylindrical spring 46 of foam material, such as polyurethane,is received within cylindrical flange 38 and engages dome spring 30 atthe opposite end.

Circuit board 48 is of conventional construction formed of dielectricmaterial which has been clad with metal 50, such as copper, and etchedto provide desired circuitry which includes a conductive means such asfixed condenser target plate 52. This may be coated withv suitablematerial 54, forming an electret, as fully disclosed in the applicationreferred to and which, per se, forms no part of the present invention.Conveniently movable plate 30 is connected to an output lead 56 andstationary plate or target is connected to a second output lead 58 forproviding an output signal when ,push button 40 is depressed in a mannerdescribed in above-mentioned U.S. Pat. No. 3,653,038.

FIG. 9 illustrates an alternative form of fixed target comprising acentral element or plate 520 and concentric ring-shaped elements orplates 52b,52c. The advantage of this construction over the pie-shapedsegments referred to resides in the generation of more uniform signals.This may be better understood if it is assumed that the symmetry ofcollapse of a dome spring may vary slightly during its successiveoperations. If it varies with the use of segmental targets, then thespacing and capacitance between each segment and the spring will alsovary. If the symmetry of collapse varies with concentric targets,however, the average spacing of the plates remains substantiallyconstant, thus producing substantially uniform signals.

As so far described, areas 18 are flat and the arcuate zone 12therebetween is of spherical radius. In the absence of extensiveexperimentation it cannot be definitely stated exactly how criticalthese shapes are. For example, the flat shape might depart somewhat froman exact flat surface and the spherical zone might depart somewhat froman exact spherical radius. It is thus contemplated, within the purviewof the invention, that the language of the appended claims beconstructed within the purview of the concepts of the invention, ratherthan their precise definitions, as set forth by dictionary definitions.

What is claimed is:

l. A curved snap-action movable sheet metal spring plate for asnap-action switch, said spring plate being in the form ofa hollowgeometric solid connectable to circuitry responsive to the snap-actionswitch, said spring plate comprising:

an open polyagonal base having a plurality of sides;

a plurality of planar side walls, one of said side walls extending fromeach side of said base at equal angles thereto and toward each other; 1

an arcuate surface interconnecting said side walls;

and

an arcuate corner interconnecting each pair of adjacent sides of saidbase and being bent to extend from said sides of said base in adirection generally opposite to said side walls.

2. A movable spring plate, as claimed in claim 1,

wherein:

said polygonal base is triangular; and

said arcuate base is spherical.

3. A snap-action switch comprising a curved spring plate as defined inclaim 1 and further including:

a flat stationary plate conductive means positioned adjacent to andspaced from said curved spring plate, said curved spring plate andstationary plate conductive means being connectable to circuitryresponsive to a decrease in the spacing of said curved spring plate andstationary plate conductiv means to provide an output signal.

4. A snap-action switch, as claimed in "claim 3, wherein said stationaryplate conductive means includes. i

a circular element adjacent to and spaced from said movable plate; and

a ring-shaped element concentrically disposed with respect to saidcircular element, said circular element and said ring-shaped elementbeing connectable to separate circuitry, each responsive to a decreasein spacing with respect to said curved spring plate to providerespective output signals.

5. A snap-action switch for supplying signals to a circuit, said switchcomprising:

a flat stationary target conductive means connectable to circuitryresponsive to said switch;

a curved movable conductive plate in the form of a hollow geometricsolid connectable to the circuitry to provide an output signal thereto,said movable conductive plate including:

an open polygonal base having a plurality of sides;

a plurality of planar side walls, one of said side walls extending fromeach side of said base at equal angles thereto toward each other;

an arcuate surface interconnecting said side walls;

and

an arcuate corner interconnecting each pair of adjacent sides of saidbase and being bent to extend from said sides of said base in adirection generally opposite to said side walls, said corners supportingsaid movable conductive plate adjacent said target conductive means andspaced therefrom; and

means for applying pressure to said arcuate surface of said curvedmovable conductive plate.to abruptly decrease the distance between saidcurved movable conductive plate and said flat stationary targetconductive means to provide a signal to the circuitry in resonse to saiddecrease in distance. 6. A snap-action switch, as claimed in claim 5,wherein said flat stationary target conductive means includes:

a layer of electret material on the side of the flat plate facing saidcurved plate. 7. A snap-action switch, as claimed in claim 5, wherein:

- said polygonal base is triangular; and

said arcuate surface is spherical.

1. A curved snap-action movable sheet metal spring plate for asnap-action switch, said spring plate being in the form of a hollowgeometric solid connectable to circuitry responsive to the snap-actionswitch, said spring plate comprising: an open polyagonal base having aplurality of sides; a plurality of planar side walls, one of said sidewalls extending from each side of said base at equal angles thereto andtoward each other; an arcuate surface interconnecting said side walls;and an arcuate corner interconnecting each pair of adjacent sides ofsaid base and being bent to extend from said sides of said base in adirection generally opposite to said side walls.
 2. A movable springplate, as claimed in claim 1, wherein: said polygonal base istriangular; and said arcuate base is spherical.
 3. A snap-action switchcomprising a curved spring plate as defined in claim 1 and furtherincluding: a flat stationary plate conductive means positioned adjacentto and spaced from said curved spring plate, said curved spring plateand stationary plate conductive means being connectable to circuitryresponsive to a decrease in the spacing of said curved spring plate andstationary plate conductive means to provide an output signal.
 4. Asnap-action switch, as claimed in claim 3, wherein said stationary plateconductive means includes. a circular element adjacent to and spacedfrom said movable plate; and a ring-shaped element concentricallydisposed with respect to said circular element, said circular elementand said ring-shaped element being connectable to separate circuitry,each responsive to a decrease in spacing with respect to said curvedspring plate to provide respective output signals.
 5. A snap-actionswitch for supplying signals to a circuit, said switch comprising: aflat stationary target conductive means connectable to circuitryresponsive to said switch; a curved movable conductive plate in the formof a hollow geometric solid connectable to the circuitry to provide anoutput signal thereto, said movable conductive plate including: an openpolygonal base having a plurality of sides; a plurality of planar sidewalls, one of said side walls extending from each side of said base atequal angles thereto toward each other; an arcuate surfaceinterconnecting said side walls; and an arcuate corner interconnectingeach pair of adjacent sides of said base and being bent to extend fromsaid sides of said base in a direction generally opposite to said sidewalls, said corners supporting said movable conductive plate adjacentsaid target conductive means and spaced therefrom; and means forapplying pressure to said arcuate surface of said curved movableconductive plate to abruptly decrease the distance between said curvedmovable conductive plate and said flat stationary target conductivemeans to provide a signal to the circuitry in response to said decreasein distance.
 6. A snap-action switch, as claimed in claim 5, whereinsaid flat stationary target conductive means includes: a layer ofelectret material on the side of the flat plate facing said curvedplate. Pg,12
 7. A snap-action switch, as claimed in claim 5, wherein:said polygonal base is triangular; and said arcuate surface isspherical.